Numerous disclosures have been made in the prior art with the aim of improving the initial discharge voltage of the lithium/fluorinated carbon batteries. Illustrative of such prior art efforts to eliminate or reduce initial voltage suppression are the disclosures in the following references.
The Japanese reference, Kokali No. 76 67,921, discloses the chemical treatment of CF.sub.x with triethylamine and ammonia to increase the discharge voltage of the battery. After treatment with the amine, the material must be washed with hydrochloric acid to remove the ammonia and the residual amine, washed with water to remove the acid, and then dried in a vacuum to remove the water. While this multi-step process reportedly reduces the effects of voltage suppression, the number of steps required in the process and the chance that residual acid or water might be carried into the cell in the treated material (lithium cells are very sensitive to acids and moisture) make this approach less than desirable.
Ultraviolet light has been disclosed in Japanese reference, Kokai No. 83 26,457, as a means to partially defluorinate CF.sub.x and to reduce the suppression of the initial discharge voltage and to improve storage. In this disclosure, the CF.sub.x is soaked or "swelled" in an organic solvent and the slurry is exposed to UV radiation. This process is very time consuming as UV radiation is capable of only very slow defluorination of CF.sub.x. The effect of the residual decomposition products in the CF.sub.x sample is not reported. Another Japanese reference the follows along this same line is Kokai No. 84 86,155. In this disclosure, UV radiation is used to defluorinate CF.sub.x suspended in a solution of sodium hydroxide and methanol. Subsequent washing with water and drying are required to remove traces of the sodium hydroxide and methanol. This process is also very slow.
Another Japanese reference, Japanese No. 84 87,762, discloses the use of an aqueous solution of HI containing methanol to partially defluorinate CF.sub.x. The CF.sub.x, with a fluorine content of .gtoreq.61.3% (F:C.gtoreq.1) is partly defluorinated to give a material with a fluorine content of .gtoreq.59% (F:C.gtoreq.0.9). Subsequent washing with water to remove HF, formed by the reaction of HI with CF.sub.x, is critical. HF can be very deleterious in a lithium battery.
Irradiation with gamma rays has also been used to defluorinate CF.sub.x and improve its discharge voltage and has been disclosed in Japanese reference Kokai No. 83 05,966. This process requires a nuclear source and would not be convenient or particularly easy to carry out in a commercial setting.
An easy, rapid, and safe chemical process to eliminate voltage suppression in the Li/CF.sub.x battery system is clearly lacking. Present practice, as covered in another Japanese reference Kokai No. 82 124,865, is to partially discharge the Li/CF.sub.x cell until 10% of its capacity is expended. This procedure is claimed to reduce the effects of voltage suppression, but requires additional equipment and processing time.
Accordingly, while it is known that various chemical treatments of fluorinated carbon have been employed to improve the initial discharge voltage in Li/CF.sub.x cells, a need exists for a simple, rapid, and safe chemical treatment to effectively eliminate voltage suppression.